9 replies to this topic

[SkyfallerTac]

I currently have a 51mm redcat, a meade LX85 8" ACF (will be getting the lepus 0.62 reducer for itwhen it becomes available) and I am considering purchasing an Evostar 80ED to have a widefield/middle of the ground and narrow FOV scope set for DSO imaging. For cameras I have an ASI294MC pro and a  planetary ASI462MC...all hooked up to ASIAR Pro or to a NUC with NINA.

 

Problem is the guiding. Trying to determine which combination I should be using and I am a bit lost when it comes to the proper rations. 

 

I use astronomy tools website to figure out the guidescope/camera combination and this is what I get:

 

Main Scope: Evo80 + 294mcpro
Guide: Redcat + ASI462
= The imaging / guiding ratio is 1:1.5

 

Main Scope: Redcat + 294mcpro
Guide: Evo80 + ASI462
= The imaging / guiding ratio is 1:0.26

 

Main Scope: 8" ACF (with 0.62reducer) + 294mcpro
Guide: Evo80 + ASI462
= The imaging / guiding ratio is 1:1.32

 

Main Scope: 8" ACF (with 0.62reducer) + 294mcpro
Guide: Redcat + ASI462
= The imaging / guiding ratio is 1:3.16

 

All this is trying to use what I have on hand. Not sure which ratio fits best as all I read is 1:5 or less is good but not 'how much less' so I am in a limbo.

 

I could buy a 30mm/120focal guidescope from williams optics and the asi120 mini (mono)  with which I get the following numbers on the website:

 

Main Scope: EVO80 + 294mcpro
Guide: W.O. 30mm/120focal + ASI120 mini
= The imaging / guiding ratio is 1:4.05

 

Main Scope: 8" ACF (with 0.62reducer) + 294mcpro
Guide: W.O. 30mm/120focal + ASI120 mini
= The imaging / guiding ratio is 1:8.5

 

Main Scope: Redcat + 294mcpro
Guide: W.O. 30mm/120focal + ASI120 mini
= The imaging / guiding ratio is 1:1.69

 

 

....or should I use an AOG with all these telescope combinations since the 294pro is not full frame? If so, the ASI462 work well for it or is it better to grab the ASI120 mini for the AOG?

 

 

As always, thank your for any advice  

[AmargosaSky]

Your longer FL setups might benefit from OAG if you're trying longer subs and your cem40 can guide that long, and in which case you are 1:1 and can just move that built train between scopes (assuming no backfocus issues between them) and call it a day. (And be future-proof if you start even longer FL stuff later)

 

FWIW, your existing 462 is a great guidecam, but for OAG it might not be able to achieve focus depending on where the OAG is located in the train, because the ASI hockey-puck style can't get closer to the prism than the guideport's exit.  QHY makes that sensor in the bullet-style body (QHY5iii462C), which can drop into an OAG port, and I use that reliably in various OAGs with longer FL setups up to 2800mm. 

 

If you're looking at grass-is-greener, then also check out the ASI174mm mini which has a nice big sensor (also a bullet body profile, so it can drop in an OAG port like the QHY5iii462) .  You can pair that with ZWO large prism OAG (recently released) to take advantage of the sensor (even does well on QHY-M OAG with some sensor wasted). But with either the 462 or 174, I am rarely short on multiple guide stars at all my FLs.

Edited by AmargosaSky, 31 December 2021 - 03:21 PM.

[rgsalinger]

This problem is why I standardized on an OAG many moons ago.

 

Get a thin OAG and get a mono guide camera - try the ZWO290 - and be happy for the rest of your imaging life. Now how well you can do with an SCT and a guide scope depends on how picky you are. The redcat 51 has almost 60mm of back focus. The flattener for most refractors requires 55mm of back focus. So there's room for an OAG and an OSC like your 294C without any real issue.

 

Keep the camera and the OAG/guide camera together and you just have to move it from scope to scope - no need to refocus the guide camera. The ease of setup alone may make it worth the extra hundred dollars or so. 

 

When using a flattener you will have to put the OAG at a specific distance from it but you're going to need some spacers anyway, the 12mm or so that a thin OAG takes up won't be an issue. Make sure that you read about the correct way to set up an OAG. It's not that hard if you do a bit of research in advance. 

 

Rgrds-Ross

[rgsalinger]

It's useful to understand some things about guiding.

 

Modern guiding software like PHD says that it can calculate the centroid of a guide star to within 1/10 of a pixel. So, as long as your guide scale is 3 arc seconds/pixel or less you will be fine.

 

With SCT's the mirror flops unless there is a way to actually lock it down. The popular Celestron SCT's do not have mirror locks, they just add some drag to the mirror's movements.

 

Even the best guide scope system that I know of - the one that Astro-Physics sells is NOT recommended for long focal length (over 1 meter) of any kind. These guys know what they are talking about. 

 

Rgrds-Ross

[TareqPhoto]

Math math math, i always fail in that, so can't we just connect scope A to camera A and scope G to camera G and done with it?

[rgsalinger]

And that, TareqPhoto, is why I use an OAG. The focal length changes nicely as the choice of OTA changes. 

[SkyfallerTac]

And that, TareqPhoto, is why I use an OAG. The focal length changes nicely as the choice of OTA changes. 

..but which camera would be used for guiding if one goes for the OAG? Can the 462 be used for any of the mentioned main scopes or is it better to get the 120 mini to put on that AOG?

 

I have the benefit my camera is not full frame so an OAG should never be an issue to use (I hope)

 

I prefer simplicity and less headaches..so if the OAG solves the issue so be it. Just need to know what camera would work for them all  

[TareqPhoto]

And that, TareqPhoto, is why I use an OAG. The focal length changes nicely as the choice of OTA changes. 

All the time i am getting like a hair away or one step from getting OAG i read issues from some members mainly in this site that made me stepping away 4-5 steps from getting one, and then i read again how people are happy and swear about it then i am just a "Click" away from buy it and then again someone regretting using OAG and again i run away, it sounds i should get one anyway and get used to it no matter what.

[imtl]

All the time i am getting like a hair away or one step from getting OAG i read issues from some members mainly in this site that made me stepping away 4-5 steps from getting one, and then i read again how people are happy and swear about it then i am just a "Click" away from buy it and then again someone regretting using OAG and again i run away, it sounds i should get one anyway and get used to it no matter what.

Especially common for beginners, they go and buy things that are over their heads. It's steep learning curve.

You are not a beginner.

[TareqPhoto]

Especially common for beginners, they go and buy things that are over their heads. It's steep learning curve.

You are not a beginner.

For now, as people saying "If it didn't break, use it or don't break it then".

 

I am happy so far with my mini guide scope for now, i don't know later when i go larger or longer FL, i will worry later about it, but i kept asking and searching before i get or buy anything, and that helped me a lot so far, and i am still learning.

 

Thank you very much